The present invention concerns a centrifugal pump of which the housing has circular shape in the circumferential direction and which has on its circumference an exit tube commencing at an exit port tangentially with reference to the flow, and wherein the length of the exit port in circumferential direction of the housing is about .pi./4R and where the outer wall of the exit tube forms a diverging bulge on transition outward from the circumference of the housing.
Centrifugal pumps of similar type are used, for instance, in sewage pumping installations. Such cases are encountered in practice in which from the sewage pump is required a great lifting height but low volumetric flow rating. Since the sewage pump is required to have a high enough so-called transmitting capacity which enables even large solids to pass through the pump, the designing of such pumps has been nearly impossible owing to the fact that it becomes unavoidable, in consideration of the transmitting capacity, to make the outflow cross section of the pump housing altogether too large from the flow technology point of view. In order that the centrifugal pump could be induced to deliver a great lifting height, the velocity of the liquid after the impeller must also be high. Low volumetric flow rate implies that the average velocity through the outflow cross section is very low, that is merely a fraction of the velocity adjacent to the impeller, whereby in a housing of conventional design a large proportion of the flow is forced to return into the housing, under the tongue. Hereby a back flow into the housing is created which gives rise to vortex losses and acts as a brake on the liquid velocity adjacent to the impeller.